Dr. Carolyn Ecelbarger, Ph.D. who has trained as both a nutritionist and a renal physiologist is in a unique position to bridge the gap between these fields. Her long-term career goals include investigating how nutritional factors affects renal function and especially how this relates to expression and regulation of salt and water transporters of the kidney. The mentored Research Career Award (KO1) will provide the proposed mentee, Dr. Ecelbarger, with the opportunity to broaden her training in physiology, under the guidance and expertise of Dr. Joseph Verbalis (proposed mentor), at Georgetown University. During her post-doctoral training at the National Institutes of Health in Dr. Mark Knepper's laboratory, her research focussed mainly on understanding those proteins which are important in the urinary concentrating mechanism, including the renal aquaporins and the Na- K-2Cl cotransporter. A key project of Dr. Ecelbarger's, done in collaboration with Dr. Verbalis' laboratory, involved assessing the role of aquaporin expression in the physiological phenomenon of vasopressin escape. Patients with this disorder initially retain water and become hyponatremic. However, if water loading continues, eventually they begin to excrete larger volumes of fairly dilute urine, despite the high circulating levels of vasopressin. This process of "vasopressin escape" has puzzled renal physiologists for decades, although little is actually understood about the mechanisms involved. In a rat model, Ecelbarger et al. were able to show dramatic down-regulation of aquaporin-2 protein, a critical protein in water homeostasis. Naturesis is another physiologic component of vasopressin escape of which little is understood. Thus, the specific aims of the proposal are summarized as follows: (1) to evaluate changes in renal expression and cellular distribution of sodium transporters during physiologic "escape" from the antidiuretic action of vasopressin; (2) to investigate signaling events involved in regulation of aquaporin-2 expression in models of vasopressin escape and chronic vasopressin exposure and (3) to assess the impact of long-term parenteral nutrition (TPN) on the expression and regulation of renal salt and water transporters. The main hypothesis is that direct regulation of expression and cellular distribution of several critical kidney tubule salt and water transporters is the means by which overall salt and water homeostasis is maintained in the body, despite physiological perturbations such as changes in blood vasopressin levels. The study proposals are briefly outlined for each specific aim, respectively; (1) to evaluate the time course of vasopressin escape with regard to expression and regulation of critical sodium transporters along the kidney tubule by immunoblotting and immunohistochemistry; (2) to utilize a variety of biochemical and immunolological approaches in order to assess important regulatory events in the V2-receptor/adenylyl-cyclase signaling cascade and determine how they relate to aquaporin-2 abundance; (3) to assess the effects of total parenteral nutrition on renal function, measures of renal hemodynamics, and expression and regulation of salt and water transporters in a rat model of TPN.